Electron beam generating device



Oct 1969 SHlNlCHIRO YAMAMOTO ETAL 3 7 ELECTRON BEAM GENERATING DEVICE Filed Feb. 12, 1968 2 Sheets-Sheet 1 Tiql. f

A ORNEY u JA I awur Oct. 14, 1969 SHlNlCHIRO YAMAMOTO ETAL 3. 1

ELECTRON BEAM GENERATING DEVICE 2 Sheets-Sheet 2 Filed Feb. 12, 1968 United States Patent O 3,472,999 ELECTRON BEAM GENERATING DEVICE Shinichiro Yamamoto and Hideo Mito, Tokyo, Japan, as-

signors to Nippon Electric Company Limited, Tokyo,

Japan Filed Feb. 12, 1968, Ser. No. 704,936 Claims priority, application Japan, Feb. 12, 1967, 42/8398 Int. Cl. B23k 9/24 US. Cl. 219-121 4 Claims ABSTRACT OF THE DISCLOSURE A device for vaporizing a material by means of an electron beam which includes an electron gun located in the vicinity of one pole of a magnet and a crucible for holding the material to be vaporized located in the vicinity of the other pole of the magnet, the arrangement being such that the electron beam travels along the path of the lines of magnetic force existing between the poles.

DESCRIPTION OF THE DRAWING BACKGROUND OF THE INVENTION When an electron beam is used as a heating means to melt and evaporate a metal or a dielectric or other material, the higher the temperature of the material rises, the higher the vapor pressure of the material will become. Therefore, in the region of the melting point of the material, the vapor pressure usually reaches a rather high value and, at the same time, a large quantity of gas is evolved therefrom. The vapor pressure and the evolved gas pressure presents several problems.

The vapor of the material and the evolved gas radiate outwardly from the material being melted and if there is an electron gun having a cathode and an anode in the vicinity of the vapor and gas stream, it raises the pressure and causes an electric discharge between the cathode and the anode. The evolved gas and vapor are ionized by the electron beam to become gas ions and vapor ions. These ions are drawn to the cathode by the electric field between the cathode and the anode until, finally, the electron gun may be damaged. Furthermore the material being melted is contaminated by the vapor of the filament material.

To eliminate these disadvantages, it is necessary to deflect the electron beam so that the electrons do not travel into the path of movement of the vapor material. Various practical methods of deflection have been contemplated for this purpose. These methods are classified into two types. One is the magnetic deflection type and the other is the electrostatic deflection type. FIG. 1 shows an example of the conventional magnetic deflection type device in which the electron gun is arranged so that the foregoing disadvantages are eliminated. FIG. 2 shows an example of the conventional electrostatic deflection type device for eliminating these disadvantages.

In FIG. 1, an electron beam 4 emitted toward an anode 3 from a cathode or filament 2 which is encircled by a repeller 1 is deflected by the magnetic field of a magnet 5 applied perpendicular to the direction in which the electron beam flows. The electron beam 4 then bombards a sample 7 to be evaporated which is placed on a crucible 6. In FIG. 2, an electron beam 9 emitted from a cathode or filament 8 is electrostatically deflected by a deflector 10 to bombard a sample 12 to be evaporated which is placed on a crucible 11. In these conventional devices shown in FIGS. 1 and 2, magnetic pole pieces or deflectors protrude above the crucible, so that a part of the material deposits on them. When there is a volume of continuously or semi-continuously evaporated material, the material deposited on the magnetic pole pieces or deflectors will form a layer having more than a certain specific thickness. This deposited material peels or flakes 01f, causing a short-circuit between the cathode and the anode during operation, or disturbing the potential distribution, thus changing the stream of the electron beam and as a result, the electron beam bombards a part other than the material to be evaporated, to eventually destroy the bombarded part.

When a thin uniform layer is to be formed by evaporation on a wide sheet in a continuous operation, it is convenient to use a narrow rectangular crucible and to move the sheet transversely with respect to the crucible. In other words, a wide and thin sheet-shaped electron beam should be employed. However, if a simple electron beam of wide dimension is to be deflected by a magnetic field, a powerful magnet must be provided and this is economically disadvantageous.

OBJECTS OF THE INVENTION An object of this invention is to eliminate the above described disadvantages and to provide an electron beam generating device employing a novel method and apparatus in which the electron beam flows along the lines of magnetic force.

All of the objects, features and advantages of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of the invention taken in conjunction with the accompanying drawing.

BRIEF SUMMARY OF THE INVENTION The electron beam generating device of this invention has its principal feature in that an electron gun having a cathode and an anode is disposed on or above one of the poles of a magnet, and a crucible is positioned on or above the other pole and, by such arrangement, the electron beam emitted from the electron gun travels generally along the lines of magnetic force directed from one pole to the other pole of the magnet and thus the material located on the crucible is melted and evaporated.

DESCRIPTION OF PREFERRED EMBODIMENTS FIGS. 3 and 4 show a first embodiment of this invention in which the electron beam generating device comprises magnets 13 and 14 which are fixed to a yoke 15, an electron gun located above the magnet 13, said electron gun comprising an anode 16, a filament 17, a repeller 18, and a filament support 19, and a water-cooled copper crucible 20 located above the magnet 14. The filament support 19 is supported by an electron gun support 23 through an insulator 21 and a filament support base 22. A heat shielding plate 24 combined with the water-cooled copper crucible 20 is provided to shield thermally the magnets 13 and 14 from the heat of the crucible. Water to be fed to the water-cooled crucible 20 is supplied thereto via water feeding pipes 26.

When a current is caused to flow in the filament 17 through the filament support 19 to heat up the filament 17 and, at the same time, a negative high-voltage is applied to the filament 17, then electrons are emitted from the filament and move along the line of magnetic force 27 by the interaction of the electric field and the magnetic field applied between the filament 17 and the anode 16. Thus, the electrons bombard the crucible 20, which is grounded. The electron beam flows in a spiral path along the line of magnetic force 27, and deviates a small distance in the lateral direction i.e. in parallel with the filament 17, the distance depending on the curvature of the lines of magnetic force, the magnetic flux density and the applied voltage. Therefore, it is necessary to shift the crucible in the lateral direction with respect to the filament 17.

According to this first embodiment, the width of the electron beam at the crucible 20 is approximately mm., and the electron beam on the whole is deviated by approximately 5 mm. in the lateral direction, under the condition that the applied voltage is kv. the magnetic flux density is 1500 gausses at the top of the beam trajectory, and the diameter of the filament is 2.5 mm.

This invention is not limited to the embodiment described above, as various modifications may be made. As shown in FIG. 5, for example, one modification comprises three magnets 28, 29 and 30, a crucible 32 placed on the magnet 29, and two electron guns 31 located on the magnets 28 and 30 which are positioned by both sides of the magnet 29. By this arrangement, the beam output can be doubled.

FIG. 6 shows another modification which comprises a hollow cylindrical magnet 34 surrounding a cylindrical magnet 33, a crucible 35 placed on the magnet 33, and a circular symmetrical electron gun 36 located on the magnet 34. By means of this structure, a large beam output can be focussed at a point on the crucible 35. In these modifications, it is necessary to select by well-known means the values of the applied voltage and the magnetic flux density so that the electron beam does not bombard any part of the structure other than the crucible.

According to the electron beam generating device of this invention, the magnet and the electron gun are positioned below the cruicible, and therefore, there is no obstacle which intercepts the vapor. Consequently, evaporated material will not form and come off to short-circuit the filament and the anode, or to change the path of the electron beam by altering the potential distribution. A wide and thin electron beam, which is necessary for forming a thin layer on a long sheet by continuous evaporation, can be readily obtained by employing a narrow electron beam emitting source and a narrow magnet having a length which corresponds to the length of the electron beam emitting source. Also, according to this invention, it is possible to dispense with any means for focussing the electron beam between the filament and the anode because the electron beam flows along the lines of magnetic force.

While the foregoing description sets forth the principles of the invention in connection with specific apparatus, it is to be understood that the description is made only by way of example and not as a limitation of the scope of the invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. An apparatus for electron beam working of materials in an evacuatable housing comprising a first longitudinally shaped magnetic yoke section,

a second longitudinally shaped magnetic yoke section spaced parallel to the first section,

a magnetic yoke plate joining the first and second yoke sections at a side thereof to form a unitary U-shaped yoke for a magnetic deflecting coil and having a longitudinal slot between the yoke sections, with the first and second yoke sections substantially terminating in a common plane,

means for providing said unitary yoke with a longitudinal magnetic field extending from the first yoke section at the common plane to the second yoke section,

an open longitudinal crucible for holding material mounted over the second yoke section above the common plane with the material in intercepting relationship with said magnetic field,

a longitudinal source of electrons located adjacent the first yoke section above said plane and below the crucible open end for heating of said material upon deflection of electrons towards the crucible by the magnetic field.

2. The device as recited in claim 1 and further ineluding a third longitudinal magnetic yoke section spaced on the other side of the second yoke section opposite the side of the first yoke section and joined to the magnetic yoke plate to form a second longitudinal slot in the unitary yoke, with the third yoke section terminating in said common plane,

and wherein said magnetic means provides a longitudinal magnetic field from the third yoke section at the common plane to the second yoke section and a second longitudinal source of electrons located over the third yoke section above the plane and below the open end of the crucible for further heating of said material upon deflection of electrons from the second source towards the crucible.

3. An apparatus for electron beam working of materials comprising a hollow cylindrically shaped outer magnetic yoke section,

an inner cylindrical magnetic yoke section located concentrically within the hollow of the outer yoke section and sized to define an annular bore between the yoke sections,

said inner and outer yoke sections being magnetically joined at one axial end of the annular bore to form a unitary yoke for magnetic deflecting coil, with the other end of the inner and outer yoke sections substantially terminating in a common plane,

means for providing said unitary yoke with a magnetic field extending from the other axial end of the outer magnetic yoke to the other axial end of the inner yoke section,

an open crucible for holding material and located on said other axial end with the material in intercepting relationship with said magnetic field,

an annular source of electrons located adjacent to and concentric with the unitary yoke above said plane and below the open end of the crucible for heating of said material of the electrons towards the crucible.

4. The apparatus as recited in claim 3 wherein the annular electron source is in registration with the outer cylindrical yoke section.

References Cited UNITED STATES PATENTS 2,932,588 4/1960 Frank.

3,105,275 10/1963 Hanks 219121 X 3,132,198 5/1964 Du Bois et al.

3,105,275 10/1963 Hanks 219l21 X 3,202,794 8/ 1965 Shrader et al 219121 JOSEPH V. TRUHE, Primary Examiner W. DEXTER BROOKS, Assistant Examiner US. Cl. X.R. 1331 

